This invention relates in general to drafting instruments, and in particular relates to instruments for drawing a family of curves such as ellipses.
Curves such as ellipses can be drawn by the use of templates having a plurality of cutouts for ellipses of different sizes and eccentricities. However, such templates have limited use because they cannot be used to draw ellipses of universal size and eccentricity.
Mechanical instruments for drawing ellipses, commonly called ellipsographs, have previously been provided. The prior ellipsographs commonly include a post on which a circular disc is mounted with the marking element carried about the post by a writing arm which contacts the edge of the disc to trace the ellipse. Eccentricity can be varied by adjustably tilting the disc relative to the post. Ellipsographs of the foregoing type have a number of disadvantages and limitations. The ellipse figures cannot be accurately drawn, especially where it is desired to draw a family of different size ellipses. A further limitation is that conventional ellipsographs, as well as templates, do not permit the drawing of ellipses having extreme eccentricities such as 5.degree. ellipses or smaller. Such prior ellipsographs are also relatively complicated and expensive to design and construct and are not readily adaptable to high-volume, low-cost manufacture.